Mixing stages or signal mixers are used in various implementations, for example in communication systems. In those applications, mixing stages may be used to mix or superimpose a baseband or intermediate frequency signal to a carrier frequency prior to the submission or sending of the generated modulated carrier frequency signal. Examples of those applications are sending or receiving stages of mobile telecommunication handsets or base stations, terrestrial radio senders and the like. Generally, mixing stages are used in multiple applications where an information signal is to be transmitted or received by means of wireless or wired transmission techniques.
One particular quality criterion for a mixing stage is the achieved signal quality, for example in terms of a spectrum of the signal provided at an output of the mixing stage. For example, it may be required that a modulator circuit for providing a single-side band modulated signal (SSB) provides a spectrum showing only the single transmitted side band without spectral components of the carrier frequency or the complementary side band. To this end, Hartley Modulators are sometimes used, inherently providing carrier suppression and suppression of one of the two side bands due to its concept. Further, mixer stages such as for example Gilbert Cells are sometimes used, which may also provide for an inherent suppression of the carrier or local oscillator (LO) frequency. Those type of mixer stages or modulators are, therefore, also called balanced devices.
Mixing stages typically comprise multiple semiconductor devices, for example bi-polar transistors or field-effect transistors, which have slightly different characteristics due to process fluctuations. Due to those differences within the participating components and also due to fluctuations within the signals used as an input to the modulation stages, also balanced devices may require some additional circuitry in order to counterbalance the imbalances present.
However, additional balancing circuitry may be costly in terms of area and production costs, in particular when the imbalances shall be counterbalanced with a high accuracy. The cost and complexity of such balancing circuitry should be reduced.